The deal concludes 20 months of negotiations, with final talks taking place since June in Vienna. The P5+1 group of the United States, Britain, France, China, Russia and Germany will all relieve oil and financial sanctions against Tehran. In return, Iran will scale back its nuclear activities to ensure it cannot build a nuclear weapon.

One major obstacle during negotiations that was finally overcome was a compromise over the inspection of Iranian nuclear sites. UN inspectors will be allowed to monitor military sites, but Iran can challenge requests for access.

The West has long been concerned that Iran holds ambitions to build a nuclear bomb. But Tehran has always maintained that its nuclear programme is purely to generate energy for civilian purposes.

The deal is regarded as a major victory for diplomacy between Iran and the West. But it has angered other parts of the middle east, including Israel and Saudi Arabia, who believe Iran cannot be trusted.